1. Field of the Invention
The present invention relates to a microstructured sensor for the detection of IR radiation.
2. Description of Related Art
Microstructured multichannel infrared sensors are used in particular as spectroscopic or photometric gas sensors, in which a measuring channel detects the intensity of the incident IR radiation of the gas-specific measuring wavelength range and a reference channel detects the intensity of the incident. IR radiation of a reference wavelength range.
For this purpose, photometric gas sensors generally have an IR radiation source, an absorption section for receiving a gas mixture to be studied, and an infrared detector having bandpass filters for the wavelengths. In general, at least one absorption band of the gas to be detected is in the measuring wavelength range, such as a carbon oxide COx or nitrogen oxide NxO; no noticeable absorption preferably occurs due to a gas in the reference wavelength range. In addition to the use as spectroscopic gas sensors, microstructured infrared sensors may further also be used as thermoelements for temperature measurement.
Published German patent application document DE 10 2007 021 911 A1 discloses a gas sensor of this type, which is implemented in microstructured form on a sensor chip. For this purpose, a measuring diaphragm is implemented cantilevered over a cavity of the sensor chip in the measuring channel, which has an absorber layer for absorbing the incident IR radiation on its upper side, for example, and thus heats up as a function of the IR radiation. The reference channel is similarly constructed having a reference diaphragm over a cavity and in general largely symmetrically to the measuring channel, in order to allow identical measuring conditions for the reference measurement as much as possible.
A sensitive structure for the detection of the IR radiation or the heating caused by the IR radiation is implemented on each of the diaphragms, the sensitive structure being able to be implemented, for example, as a bolometric, a pyroelectric, or as a thermopile structure having a series circuit of multiple thermocouple pairs made of two thermopile legs each. In each channel, the thermopile legs are implemented from materials having different Seebeck coefficients and extend from the bulk material outside the diaphragm to the diaphragm, contacting with one another in hot contacts on or in the diaphragm and in cold contacts in the bulk area, so that hot and cold contacts are implemented alternately in the series circuit. The temperature of the diaphragm of each channel is thus ascertained as a difference in relation to the bulk material, an appropriately strong measuring signal being able to be obtained by the series circuit of a high number of thermocouple pairs.
The two thermopile measuring structures thus convert the heating of the particular diaphragms into electrical voltages, so that two measuring signals are output, from which the gas concentration may be ascertained.
Such a construction of a spectroscopic sensor or gas sensor thus requires a suitable space requirement on the sensor chip as well as the space requirement and processing complexity of implementing contact pads and the contacting of the sensor chip, in order to read out the measuring signals.